The invention relates to a shifting device for a transmission unit, in particular for a vehicle which is operated by muscle force, having a shaft, on which a plurality of loose wheels is mounted which, with a corresponding plurality of gearwheels, form wheel pairs of at least one partial transmission, wherein the shaft is formed as a hollow shaft and the loose wheels can be connected to the shaft by means of selecting means, wherein the selecting means can be actuated selectively by means of at least one camshaft mounted in the hollow shaft in order to form gear stages of the partial transmission.
The invention furthermore relates to a transmission unit, in particular for a vehicle driven by muscle force, having a shifting device of this kind.
Finally, the invention relates to a method for shifting the abovementioned shifting device.
Such shifting devices and transmission units are used to gear up or gear down driving force, in particular muscle force, and thereby make the vehicle easier to drive.
U.S. Pat. No. 5,924,950 A discloses a bicycle transmission of this kind. This bicycle transmission has an input shaft and a countershaft, wherein a plurality of driving wheels is mounted on the input shaft and a corresponding number of selectable driven wheels is mounted on the countershaft. The selectable gears on the countershaft are selected by means of a plurality of axially movable selector pins and free-running clutches arranged in the countershaft, wherein the countershaft is connected to a pinion as the output member of the bicycle transmission by means of a planetary transmission. The pinion is connected to the sun wheel of the planetary transmission by a clutch, and the annulus of the planetary transmission can be blocked or fixed by means of a Bowden cable. The planetary transmission thereby forms a two-speed transmission, which is connected in series with the seven-speed transmission on the countershaft, thus allowing fourteen gears to be formed by means of the bicycle transmission as a whole. The disadvantage with the system is the axially large form of construction and the relatively small number of fourteen gears that can be formed. It is furthermore disadvantageous that the two partial transmissions must be activated separately and therefore have to be operated with an increased effort. In this context, it is furthermore disadvantageous that the two partial transmissions are not matched to one another and hence that sequential shifting through all the gears and, in particular, simultaneous shifting of both partial transmissions is inconvenient.
DE 10 2008 064 514 A1 discloses another transmission unit for a vehicle driven by muscle force, having an input shaft, an output shaft and a countershaft, wherein a plurality of loose wheels is mounted on the countershaft which, with gearwheels on the input shaft or the output shaft, form wheel pairs of two partial transmissions, and wherein the loose wheels can be connected for conjoint rotation to the countershaft by means of selectable free-running clutches, wherein the free-running clutches can be actuated by means of two separate camshafts. In this case, control of the two camshafts by two separate planetary transmissions is associated with a corresponding space requirement and an additional outlay on control for synchronization of the two partial transmissions.
It is therefore the object of the present invention to provide an improved shifting device and an improved transmission unit for a vehicle driven by muscle force, which unit has a compact form of construction, has improved shifting convenience and can be implemented with low technical effort.